1. Field of the Invention
The present invention relates to the field of detectors designed for detecting non-authorized objects in a zone having protected access.
The present invention applies in particular to detecting metal objects.
2. Description of Related Art
Nowadays it is found to be necessary to check with a very high degree of reliability for attempts at introducing or removing non-authorized objects into or from a sensitive zone.
When posed in this way, the problem covers a very wide range of situations, and in particular but in non-limiting manner, it covers detecting objects stolen from stores, businesses, or warehouses, and attempts at introducing dangerous objects into protected zones such as stores, schools, stations, and public or private organizations.
Numerous means have already been proposed for performing such detection.
In particular, numerous metal detectors have already been proposed.
Examples of known detectors, and in particular metal detectors are to be found in the following documents: FR-2 720 519, FR-2 775 350, FR-2 780 585, FR-2 694 098, FR-2 697 919, FR-2 698 178, FR-2 698 968, FR-2 608 286, FR-2 610 417, FR-2 607 937, FR-2 608 286, FR-2 607 937, U.S. Pat. No. 6,362,739, U.S. Pat. No. 6,359,582, U.S. Pat. No. 6,344,818, U.S. Pat. No. 6,342,696, U.S. Pat. No. 6,218,830, U.S. Pat. No. 5,790,685, U.S. Pat. No. 5,680,103, U.S. Pat. No. 5,341,126, WO03/032 011, US-2001 0 042 412, WO98/12 573, WO97/50 000, WO97/42 527, EP-0 740 822, EP-0 490 921, WO91/03 746, U.S. Pat. No. 5,121,105, WO88/07 733, US-2003 0 142 853, US-2003 0 128 150, U.S. Pat. No. 6,507,309, U.S. Pat. No. 6,507,278, US-2002 0 130 804, U.S. Pat. No. 6,359,582, U.S. Pat. No. 6,150,810, U.S. Pat. No. 6,133,829, U.S. Pat. No. 5,726,628, U.S. Pat. No. 5,600,303, U.S. Pat. No. 5,692,029, U.S. Pat. No. 5,689,184, U.S. Pat. No. 5,227,800, U.S. Pat. No. 5,073,782, U.S. Pat. No. 5,039,981, U.S. Pat. No. 4,866,439, U.S. Pat. No. 4,866,424, U.S. Pat. No. 4,263,551, U.S. Pat. No. 4,019,053, U.S. Pat. No. 4,012,690, U.S. Pat. No. 3,971,983, U.S. Pat. No. 3,707,672, U.S. Pat. No. 4,987,767, U.S. Pat. No. 5,109,691, U.S. Pat. No. 4,449,115.
More precisely, it is found nowadays that people attempting to remove objects fraudulently from a protected zone, e.g. a thief stealing from a store or a business, or people attempting to introduce prohibited objects, e.g. a school child attempting to introduce an object into a school, are making ever-increasing use of shoes and/or socks for hiding the objects in question.
This phenomenon seems to be due essentially to the fact that this zone of the human body is not easy to inspect visually or by touch.
Furthermore, experience shows that known conventional devices generally give rise to higher alarm rates at shoe level than when acting on the remainder of the human body, apparently because of the almost universal presence of metal reinforcement in the narrow or “shank” part of the soles of shoes.
Attempts have indeed been made to develop detectors that are specifically dedicated to detecting prohibited objects in the shoes of individuals.
Examples of such devices are to be found in documents U.S. Pat. No. 5,039,981 and EP-0 978 734.
However, in practice, none of the devices that have been proposed in the past gives total satisfaction.
Thus, on some sensitive sites it is nowadays necessary to make use of X-ray inspection apparatus, thus requiring people leaving the site or entering the site to remove their shoes, since X-rays devices should not be used directly on shoes that are still being worn because that would lead to exposing parts of the human body to ionizing radiation.